Technical Field
The present invention relates to a method of preparing sodium bentonite. Specifically, calcium bentonite is converted into sodium bentonite by a combination of chemical, thermal and mechanical treatment procedures. The produced sodium bentonite is suitable for but not limited to oil and gas drilling and cementing applications.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Bentonite is a natural clay consisting primarily of montmorillonite that is usually formed from weathering of volcanic ash in the presence of water. There are different types of bentonite, each named after the respective dominant element, such as potassium (K), sodium (Na), calcium (Ca), magnesium (Mg) and aluminum (Al).
Na-bentonite expands up to 15 times its volume when wet, adsorbing as much as several times its dry mass in water. The excellent colloidal and adsorbent properties of Na-bentonite have popularized its use, compared to other types of bentonite, in drilling mud or drilling fluid for oil and gas wells and boreholes for geotechnical and environmental investigations. Na-bentonite is used as a viscofier or lubricant and in water control to reduce filtration loss. Further, the mixing of Na-bentonite in the drilling fluid helps to cool the cutting tools, to remove the soil and rock cuttings, to support the borehole and to prevent it from collapsing through the formation of a mud cake. Most high-grade natural Na-bentonite in the United States, which is the world's largest bentonite producer, is produced from the western part of the country in area between the Black Hills of South Dakota and the Bighorn Basin of Wyoming. In addition to drilling fluid applications, Na-bentonite is also useful as a sealant, providing a self-sealing, low permeability barrier, for example, at the base of landfills.
Ca-bentonite, which is found abundantly in the southern part of the United States such as Mississippi and Alabama, also has good adsorbent properties but is only capable of swelling 2-3 times of its unwetted volume.
Researchers and bentonite producers have attempted to utilize their local resources of bentonite. For example, different methods have been used to purify or treat raw bentonite, such as dry-sieving, wet-sieving, dispersing in hexametaphosphate solutions, sedimentation and mixing with soda ash. These attempts have been found to be time-consuming or have low efficacy:
Al-Homadhi et al. attempt to treat local bentonite with soda ash and to upgrade the treated bentonite with extenders or additives such as salt and polymers. The final modified bentonite did not satisfy API specifications for evaluation of drilling mud (Al-Homadhi, E. S. “Improving Local Bentonite Performance for Drilling Fluids Applications”, Society of Petroleum Engineers Saudi Arabia Section Technical Symposium, 7-8 May 2007, Dhahran Saudi Arabia—incorporated herein by reference in its entirety).
In Australian Pat. No. AU566345B (incorporated herein by reference in its entirety), magnesium- and/or calcium-containing bentonite are agglomerated by soda ash treatment to produce Na-bentonite for laundry applications. The produced Na-bentonite has not been evaluated for drilling fluid applications.
Chinese Pat. No. CN1061946C (incorporated herein by reference in its entirety) describes a process of producing Na-bentonite from Ca-bentonite by soda ash treatment followed by ion exchange reaction. The produced Na-bentonite also has not been evaluated for drilling fluid applications.
Yildiz et al. activate local Ca-bentonite with soda ash to increase the Na/Ca ratio and disperse the activated bentonite in sodium hexametaphosphate solutions to increase the stability of the suspension. The rheological properties of the activated bentonite are tested at different sodium hexametaphosphate and NaCl concentrations but not according to the API standards for drilling fluids (Yildiz, N., Sarikaya, Y., çalimli, A. “The effect of the electrolyte concentration and pH on the rheological properties of the original and the Na2CO3-activated Kutahya bentonite” Applied Clay Science 14(5-6):319-327, 1999—incorporated herein by reference in its entirety)
Kaufhold et al. activate Mg/Ca-bentonite with sodium carbonate (soda ash) in both dry state and in solution with excessive water with no heating. The authors conclude that despite the addition of the sodium carbonate in excess (1-5 wt. %), the activation process whether it is conducted in a dry state or a wet state may be incomplete and partial (Kaufhold, S., Emmerich, K., Dohrmann, R., Steudel, A., Ufer, K. “Comparison of methods for distinguishing sodium carbonate activated from natural sodium bentonites” Applied Clay Science 86:23-37, 2013—incorporated herein by reference in its entirety).
Karagüzel et al. activate local bentonite with 1.5-3 wt. % soda ash and 0.5% MgO without heating and a prior purification step. The combination of soda ash and MgO is found to influence the viscosities, swelling indices and filtration losses to produce an activated bentonite that satisfies drilling mud standards (Karagüzel, C. çetinel, T., Boylu, F., çinku, K., çelik, M. S. “Activation of Na, Ca)-bentonites with soda and MgO and their utilization as drilling mud—incorporated herein by reference in its entirety).
In view of the foregoing, it is evident that treatment of raw non-sodium bentonite with soda ash alone can only improve characteristics such as swelling to a limited extent that would not suffice for oil and gas drilling applications. Accordingly, it will be beneficial to provide methods of producing Na-bentonite from local, raw Ca- and/or Mg-bentonite for drilling mud applications. Preferably, a minimal number of additive compounds is added to the raw bentonite to modify the rheological properties so that the produced Na-bentonite maintains a high purity.